Researches on new polymer materials are carried out in order to confer improved functionalities, including thermal, mechanical and electrical properties. In this regard, development of new hybrid materials consisting of organic and inorganic components is drawing attentions.
The most important considerations in the designing of organic/inorganic hybrid materials meeting such technical requirements are compatibility between organic and inorganic polymers, thermal stability, or the like. Polysilsesquioxane with high heat resistance is viewed as a solution material that can solve the technical requirements. With superior physical and chemical properties, polysilsesquioxane materials are widely used in the form of oil, rubber, resin, etc. for heat-resistant, weather-resistant and impact-resistant packages, seals, insulations, lubrication, semi-gas permeable coatings, or the like. They are extremely important polymers in the industries.
However, it has not been commercialized on a large scale since the structure of polysilsesquioxane is not fully elucidated and the control of molecular weight is difficult.
In general, polysilsesquioxane is synthesized by hydrolysis hydrolysis polymerization. At present, hydrolysis polymerization using trialkoxysilane (RSi(OR)3) or trichlorosilane (RSiCl3) is widely known. Formerly, it was thought that thus synthesized polysilsesquioxane generally has a perfect ladder structure. However, with the development in chemical analysis technique, it is known that it has an imperfect cage structure or a low molecular weight, irregular structure with a weight average molecular weight 5,000 or smaller.
For these reasons, the expected solubility and mechanical or physical properties are not attained. Since the synthesis of polysilsesquioxane with a perfect ladder structure having superior solubility in general organic solvents is very difficult, organic/inorganic hybridization of polysilsesquioxane is mainly performed by the sol-gel method. A lot of experimental data are presented to overcome these problems.
As an existing art, a method of converting incompletely condensed silsesquioxane, which results from a general condensation reaction, into one having a cage structure in the presence of an excess base catalyst is reported. However, this method is not practically applicable since a complete cage structure or ladder structure is not attained. In particular, there are few cases of reported application for monomers having bulky side chains (Patent Reference 1: Japanese Patent Laid-Open No. 2003-510337).
Further, as an existing method for preparing silsesquioxane, a method of performing condensation at high temperature for long hours in the presence of a base catalyst is known. However, the reaction at high temperature for long hours consumes a lot of energy and, although the degree of condensation is relatively high, it is still insufficient (The alkoxy groups remain.) (Patent Reference 2: Japanese Patent Laid-Open No. 2004-354417).
Two-stage condensation was proposed to overcome the problems of the above methods. It aims at preparing silsesquioxane with higher T3 structure ratio through a two-stage reaction of polymerization followed by dehydration at high temperature. However, the complicated process is not readily applicable to the industrial fields (Patent Reference 3: Japanese Patent Laid-Open No. 2004-002663).
Besides, copolymers obtained from silsesquioxane derivatives are reported in several literatures. They aim at crosslinking silsesquioxane having an imperfect cage structure with a difunctional siloxane compound. However, the resulting polysilsesquioxane is not structurally perfect (Patent Reference 4: U.S. Pat. No. 5,589,562).
As described, the researches on silsesquioxane thus far have not succeeded in obtaining a polymer with a perfect structure. Merely, polymerization techniques for attaining particular structures such as ladder structure or cage structure are being studied.